DiMarco, who hasn't won on the PGA Tour since 2002, has been playing with arthritis, tendinitis and a bone spur in his left shoulder for about three months. Two recent cortisone shots and a slight adjustment to his swing seemed to ease his pain. The 64 was his best round of the season.
``It felt a lot better out there today,'' he said. ``Three weeks ago, every shot I hit, whether it was a 70-yard lob wedge or whatever, it would pop.''
Five golfers finished at 65, including Tour rookie Michael Sim of Australia, who shot 29 on his closing nine.
``Once you get on a roll, you just make birdies,'' Sim said.
DiMarco said he tinkered with his putting grip, which seemed to help his short game. He needed just 26 putts.
``I made a bunch of good little putts today,'' he said. ``When you make those, confidence breeds and you make longer ones.''
The best shot Thursday came from Craig Perks of New Zealand, who used a 6 iron to ace the 202-yard par-3 eighth hole. His blind tee shot went over the water and rolled into the cup.
Perks, who shot a 74 in the first round, took home a gold Rolex watch for his effort. Defending champion J.J. Henry, from nearby Fairfield, shot a 68.
Masters champion Zach Johnson shot a 71 and Vijay Singh a 68. Singh entered the tournament in third place in the race for the Fedex Cup. He has a chance to make up ground on Tiger Woods and Mickelson.
